Carbon dioxide has been blamed as a primary cause for global warming and is mostly discharged from using fossil fuel. As carbon dioxide is a carbon compound having the lowest energy, input of energy is necessary to convert it into a useful resource, and to this end, various types of energy sources such as hydrogen energy, solar energy and electric energy can be used. Especially, by using the conversion of carbon dioxide using electric energy can convert carbon monoxide, formic acid, methanol, methane, oxalic acid, and others can be converted into various organic compounds by using an electrode reaction under a condition of a room temperature and an atmospheric pressure depending on types of electrode materials and reaction conditions. In this case, since potential differences of reduction of carbon dioxide and generation of hydrogen in an aqueous solution are very close to each other, and the reduction of carbon dioxide is interrupted by the competition of the two reactions, it is necessary to use an electrode having a large overpotential to the generation of hydrogen and a catalyst or electrode surface for selectively converting only carbon dioxide. Thus, as useful materials for the electrode, materials having a large overpotential to the generation of hydrogen have been mostly used. It has been reported that when Hg, In, Sn, Pb, or others are used as an electrode, conversion efficiency into formic acid is high, whereas in case of Zn, Au, Ag, or others, selective conversion efficiency for carbon monoxide is high. Results from using a mercury (Hg) electrode have been reported since 1960s, and it has been reported that when current density is 1 mA/cm2 while using a Hg pool electrode, formic acid is produced with 100% current efficiency. When a Zn amalgam electrode was used, 88.6% current efficiency was achieved for formic acid, and when a Pb amalgam electrode was used, conversion into formic acid was achieved with 90% or more efficiency. In recent, it has been reported that when a Sn electrode is used, formic acid is produced with 63% efficiency. Most electrode materials useful for the conversion into formic acid, except for mercury, cannot be used for a long time due to deactivation of electrode materials themselves. Mercury is advantageous in that since it has the highest hydrogen overpotential, it can achieve the highest efficiency in converting carbon dioxide into formic acid, and furthermore, be stably used for a long time. However, since mercury exists in a liquid state at a room temperature, it is difficult to deal with mercury, and furthermore, if continuously exposed to mercury, toxicity effects such as neural damage and eyesight loss occur, which results in a social environment without using mercury if possible. Thus, people are in the social atmosphere that does not use the mercury if possible. Amalgam is an alloy with mercury, and there are various types of amalgam, among which dental amalgam is being currently used for human beings' oral cavity and assures its safety. Although there have been several attempts to use dental amalgam as an electrode material in the meantime, all the attempts used the dental amalgam for a short-time analysis such as heavy metal analysis using a cathode potential stripping analysis [Korean Patent Application Publication No. 10-2005-0024547].